Mari Veliz (ABCA)-Data and models, combined, help tell the story of future and past agri-environmental decisions helping us to understand how we can make a difference

Contact Mari Veliz: mveliz@abca.on.ca

Presentation Video:

Since 2010, the Ausable Bayfield Conservation Authority (ABCA – Mari Veliz, Brynn Upsdell Wright and Ross Wilson), the Huron County Federation of Agriculture (HCFA, Joe Vermunt), the University of Guelph (Dr. Wanhong Yang, Elizabeth Jane Simmons and Yongbo Liu) and the Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs (Gabrielle Ferguson, Kevin McKague, Stewart Sweeney, and Jacqui Empson Laporte) examined the environmental effectiveness and economic costs and benefits of agricultural best management practices (BMPs) in four study watersheds. The Watershed Based Best Management Practices Evaluation (WBBE) project required the year round collection of water samples during rain fall events and base flow conditions. (Typically the ABCA collects water samples from around the basin on a monthly schedule from March to November.)

An important finding from the study highlighted the increase in concentrations of total suspended sediment, total phosphorus (shown here) and soluble reactive phosphorus during rainfall events. According to the Soil and Water Assessment Tool, channel erosion (including short-lived in-field channel erosion) accounted for the majority of the loss. Water cuts channels across the landscape and transports nutrients and sediment. Upland water is also causing downstream erosion. Best management practices (BMPs) need to address these processes. Evaluation of typical land BMPs is potentially limited during routine monitoring programs that do not include sampling during rain fall and rain on snow events.

The WBBE project provided some insights into evaluating five different BMPs (conservation tillage, cover crops, nutrient management, water and sediment control basins and a grassed filter strip) and I will share some main points with you in the following case study. But if you would like more information please see http://www.abca.on.ca/page.php?page=crops-and-creeks-huron

We found that it was easier to measure the effectiveness of structural BMPs (i.e., Water and Sediment Control Basins and grass filter strip) than management BMPs at the field scale. The case study depicted here shows a 5 m wide grassed ditch. This grass strip filters runoff from a 3-hectare area of the 12-hectare field. Water quality was measured at two locations, one at the edge of the field and one at the outlet of a culvert that drains the grass filter strip. Water samples from rainfall or snowmelt events were collected in bottles embedded into the ground. Water samples were transferred to laboratory sample bottles and analyzed for nutrients and suspended sediment. Surface runoff samples showed declines in total phosphorus (TP), soluble reactive phosphorus (SRP), and total suspended solids (TSS) after the runoff had passed through the grass filter strip. On average, TP declined by 47 per cent, SRP by 63 per cent, and TSS by 48 per cent during runoff events between June 2011 and March 2012. Nitrate, on the other hand, did not show consistent declines as runoff passed through the filter strip. In fact, in several instances, nitrate concentrations were higher downstream of the filter strip than upstream. These results suggest that a grass filter strip can effectively reduce phosphorus and sediment in surface runoff from a 3-hectare area of cropland.

Upon showing the results of the phosphorus reduction from the filter strip to the participating landowner, the hay field was extended (as shown in the bottom picture). This change in land management, from a cropped field to a hay field, resulted in the elimination of a concentrated flow path. The lack of a flow path meant that no water samples could be collected. Without the flow path, sediment and phosphorus were not transported. When the soil was covered, the development of rills and gullies in the field was reduced. A helpful framework for thinking about the role of the landscape level BMPs was proposed by Tomer et al. 2013. In this paper, we see a hierarchy of BMPs and activities, with BMPs that cover the soil and build soil health being the fundamental types of BMPs.

The implications of the change in land management, in this case from a cropped field to a hay field extend to the downstream channel. Without the excess water, there is potential for there to be reduced downstream channel erosion. Changes in water flow over multiple fields throughout a watershed is difficult to capture with traditional monitoring techniques. Likewise, we found it difficult to measure the effectiveness of the other management practices, cover crop, nutrient management, and conservation tillage at the field-edge or watershed scale. One of the challenges of our current monitoring (even if we did target rain fall and rain on snow events, which we typically do not) is that samples cannot separate the different layered BMPs and other land use activities upstream. However, the SWAT model was able to account for these management changes at the field-edge and watershed outlet. This process-based model was able to compare the different BMPs relative to each other. The SWAT model results highlighted the importance of the management BMPs.

The landowner of the depicted field plans to return to row crops in 2015. The landowner felt that the hay productivity was going to go down, unless he fertilized the field. His feeling was that it did not make economic sense (to fertilize the hay field), “even if it was better for the creek” (to leave the hay field). The management practice implemented in this case is a short term crop income economic decision.
When we look over time at the landscape in the next nine (9) slides we can see the landscape implications of year by year economic and time management decisions. As farmers strive to maximize income and efficiency, the result is field size, row crops and tiling increase while wind breaks and forage crops decrease.